In economics, what measure shows the percentage change in quantity demanded after a one-percent price change?

Price elasticity of demand measures the percentage change in quantity demanded after a one-percent change in price.

It is commonly calculated as the percentage change in quantity demanded divided by the percentage change in price. Because price and quantity demanded usually move in opposite directions, the result is often negative, although economists frequently discuss its absolute value.

Demand is called elastic when the absolute elasticity is greater than one, meaning quantity responds proportionally more than price. It is inelastic when the absolute value is less than one, and unit elastic when the absolute value equals one. Products with close substitutes often have more elastic demand.

Elasticity is not the same as the slope of a demand curve. Slope depends on the units used, while elasticity uses percentages and is therefore unit-free. It also helps predict revenue: with elastic demand, a price increase tends to reduce total revenue; with inelastic demand, it tends to increase it.